Patent EA-000704-B1 (EA)
Title: Lubricating oil dewaxing with membrane separation
Inventor: KLOSZEWSKI HAROLD A
IPC: B01D61/02
Filed: 1997-04-02
Abstract: 1. A semicontinuous process for solvent dewaxing a waxy petroleum oil feed stream comprising the steps of diluting of the waxy oil feed stream with solvent; cooling the waxy oil feed stream in successive heat exchange stages; feeding the oil/solvent/wax mixture to a filter to remove the wax and obtain an oil/solvent filtrate stream, contacting the oil/solvent filtrate stream at a temperature of -35 degree C to +20 degree C with one side of a selective semipermeable membrane in a membrane module to selectively transfer solvent through the membrane to obtain a solvent permeate stream on the other side of the membrane, the oil/solvent filtrate stream side of the membrane is maintained at a positive pressure relative to a pressure on the solvent permeate side of the membrane, and wherein the volume ratio of solvent in the permeate stream to retentate stream is 1:1 to 3:1; selectively transferring a major amount of solvent from the filtrate side of the membrane to the solvent permeate side of the membrane, and recycling the solvent permeate at a temperature of -35 degree C to +20 degree C to the filter feed; withdrawing a solvent-lean filtrate stream containing the remaining solvent from the filtrate side of the membrane module, contacting the filtrate stream by indirect heat exchange with the warm waxy oil feed; treating the withdrawn filtrate stream to recover the remaining solvent from the oil; recovering a dewaxed oil product stream and a wax product; and periodically directing a warm stream of recovered solvent onto the membrane surface to wash the membrane and remove impurities therefrom. 2. The process of claim 1 wherein the dewaxing solvent comprises a mixture of methyl ethyl ketone and toluene (MEK/tol.) and the ratio of MEK:tol. is 60:40 to 80:20 parts by weight. 3. The process of claim 1 wherein the waxy oil feed is a heavy neutral lubricating oil stock having a boiling range of 454 to 566 degree C. 4. The process of claim 1 wherein the waxy oil feed is a deasphalted lubricating oil stock having a boiling range of 566 to 704 degree C. 5. The process for solvent dewaxing a waxy petroleum oil feed to obtain petroleum oil lubricating stock comprising the steps of: treating the waxy oil feed with cold solvent to crystallize and precipitate wax particles, thereby forming a multiphase oil/solvent/wax mixture containing filterable wax particles, filtering the multiphase mixture to remove filterable wax particles from the cold oil/solvent/wax mixture to recover a cold wax cake and a cold oil/solvent filtrate stream; the improvement which comprises: feeding the cold oil/solvent filtrate stream containing wax particles under operating pressure of at least 2750 kPa to a selective permeable membrane for selectively separating the cold filtrate into a cold solvent permeate stream and a cold oil-rich retentate stream which contains the dewaxed oil and the remaining solvent; and periodically interrupting flow of the filtrate stream to the membrane; and directing a warm stream of recovered solvent onto the membrane surface to wash the membrane and remove impurities therefrom. 6. The process of claim 5 wherein the membrane consists essentially of the polyimide polymer based on 5(6)-amino-l-(4'-aminophenyl)-1,3,3-trimethylindane. 7. The process of claim 5 wherein the cold oil-rich retentate stream contains dewaxed oil and solvent is distilled to recover dewaxed oil product and to recover the warm solvent stream for washing. 8. The process of claim therein the dewaxing solvent comprises MEK and toluene in ratio of 60:40 to 80:20 parts by weight and wherein the warm solvent stream is recovered at a temperature of 10 degree C to 50 degree C. 9. The process of claim 8 wherein periodic washing step is effected for a time period of 15 to 60 minutes following wax buildup during continuous membrane operation. 10. The process of claim 5 wherein periodic washing step is conducted at a solvent wash flow rate of 0.001 to 0.03 kg/min of solvent per square meter of membrane area. 11. The process of claim 5 wherein the permeable membrane comprises parallel banks of spirally wound membrane modules, and wherein individual module banks are washed while other banks remain on stream. 12. The process of claims 1 or 5 wherein the warm stream of recovered solvent is directed onto the membrane surface at a process pressure of at least 2750 kPa. 13. The process of claims 1 or 5 wherein the temperature of the warm stream of recovered solvent is from 4.5 to 2l degree C.